Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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AUTONOMOUS ACOUSTIC DETONATION DEVICE
FIELD OF THE I~ENTION
The present invention pertains to demolition and
particularly dekonators. More particularly, the invention
pertains to the simultaneous detonation of a plurality of
explosi~es.
BACKGROUND OF THE INVENTION
In some situatisns during ths course of
commercial and military demolition operations, it is
imperative to have substantially simultaneous detonation
of several explosive charges which are not in close
proximity to each other. Further, it is desirable that
these devices do not require any physical connections
between them, that they need not require line of sight
location, nor that magnetic wave~ interfere with their
operation. This allows the operator to place the charges
faster and conceal them better, thereby reducing the
possibility of enemy detection.
In the past, if an operator wished to destroy a
subject (e.g., a bridge), the operator would distribute
charges throughout the supporting members of the bridge.
These charges would then be connected with a detonation
cord or wire which would be strung from one charge to
another. The detonation cord and wire had two negative
characteristics. The first was that it took time to
string the cord or wire. This forced the operator to
spend an inordinate amount of time stringing the cord or
wire; the operator was thereby less efficient and exposed
to possible detection by unfriendly forces for a greater
time period. The second detrimental characteristic was
the detection of the detonation cord or wire; as the cord
or wire was strung from one charge to another, it was
difficult to conceal. Thus detection of the explosive
before detonation became ~uite probable in military
operations.
A second method of detonating devices includes
remote blasting systems. ~n example of this method is in
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U.S. Patent No. 4,615,268. This method uses an
electromagnetic wave to induce AC currents in the
receiving unit. Upon receiving the electromagnetic wave,
the receiving unit detonates a blasting cap which in turn
detonates a charge. Although this method does not US2
detonation cord, it is susceptible to electromagnetic
interferences. For instance, if the object the operator
wishes to remove was a radio tower, it was possible that
the tower itself would interfere with the detonation
methodO
The U.S. Army has a de~ice designated as the Ml
Concussion Detonator. The Ml Concussion Detonator is a
mechanical ~iring device actuated by the concussion wave
of a nearby blast. It fires several charges
simultaneously without connecting them with wire or
detonating cord. A single charge detonated in water or
air will detonate all charges primed with the concussion
detonators within a particular range of the main charge or
of each other. Thi~ device has two major drawbacks. The
first is that it requires line of sight betwe~n each
charge in order to operate. The second is that the
maximum range in air is only 25.2 feet thus severely
limiting the device. Another drawback is that the Ml is
unable to discriminate between particular types of
signals, as the Ml is dependent upon signal strength only.
This invention overcomes the problems of the
prior art. This invention does not require physical
connections between each of the charges, yet allows them
to detonate substantially simultaneously. Howev~r, unlike
the remote blasting system, this invention is no affected
by electromagnetic waves. ~his invention operates by
sensing the acoustic wave generated by the explosion of a
primary charge. Further, it has a much larger range than
the Ml and does not require a line of sight placement due
to the characteristics of an acoustic signal. Further,
unlike the Ml, this invention is capable of discriminating
between different signals, thus lessening the chance of a
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false detonation.
SUMMARY
This invention overcomes the problems previously
described in the background through use of an acoustic
sensor. This invention i6 capable of being activated by
two or more pounds of high explosives such as C4 explosiv~
at a range of 150 feet. "C4" is a designator used by the
Army to identify a particular explosive described in
lo Military Specification MlL-C-45010A. Further, this
invention does not require line of sight placement due to
the characteristics of a low fre~uency acoustic signal.
This invention comprises an acoustically sealed box
containing an acoustic sensor means, a logic means and an
output means. The acoustic sensor means comprises a
microphone, a band pass filter and a detector. The
microphone senses the acoustic signal generated by the
detonation of a primary explosive and passes this signal
to a band pass filter. The band pass filter then passes
a predetermined freguency band to the detector. I~ the
signal is of sufficient strength, the detector then passes
the signal to the logic means. The logic means comprises
a pair of oscillators, a pair of counters, a self check
means and an output control. The power source can either
be primary batteries such as carbon zinc or alkaline or
can be a reserve battery where the electrolyte is stored
in a glass ampule internal to the battery until it is
broken at activations. When electrical power is applied
to the electronics, both counters begin counting out the
predetermined time from signals provided by the
oscillators. The self check means determines whether both
oscillators are operating at similar frequencies thereby
increasing the safety of the invention. Upon both
counters reaching the predetermined time and the self
check means giving a positive signal to the output
control, a signal from the detector may pass to the output
means. This allows the operator a predatermined time from
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when he activates the invention, to the time that th~
detonator will actually operate. Further, the logic means
has a second predetermined time counted by the counter,
where upon the counter reaching the second predetermined
time, passes a fire signal to the output means. This
prevents a failure of the primary charge from preventing
the device from eventually detonating.
The output means for this invention is common in
this class of art and operates simply by applying the
energy from the energy source to a blasting cap.
Line of sight location is not required for this
invention due to the characteristic~ of a low frequency
acoustic signal. A low frequency signal is able to travel
around objects. It is therefore not necessary for
physical connections between the devices as the acoustic
sensor will sense the detonation of the primary explosive
if it is located within a specific range. Further,
electromagnetic waves will not affect the device, thus
avoiding the major faults of the related art.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure l demonstrates how a detonation device is
utilized for the destruction of a bridge.
Figure 2 is an embodiment of the invention.
Figure 3 is a schematic block diagram of the
invention.
Figure 4 is a schematic of the sensor means.
A DESCR_PTION OF THE PREFERRED EMBO~IMæN?
The development of the present invention, an
acoustic detonation system, was in response to a need at
the Engineers' School at Ft. Leonardwood, Missouri. The
detonation system was designed to be activated by the
detonation of 2 lbs. of C4 explosive at a distance of up
to 150 feet. Secondly, it does not reguire a line of
sight between the primary charge datonation and the
system. Thirdly, the system is immune from false
activation from the normal background environment.
Fourth, since broadcast towers, radat, and microwave
facilities are potential targets, the device can operate
in high RF (Radio Frequency) environments.
Figure 1 demonstrates how the present invention
may be utilized in the destruction o~ a bridye 110.
Invention or autonomous detonation device 120 having at
least 2 lbs. of the C4 explosive is placed on numerous
supporting structures o~ the hridge 110, making sure that
10 each device 120 is within the 300-foot diameter 125 of a
second device 120. This insures that each device 120 will
be detonated substantially simultaneously with explosion
of a primary charge 130. A main primary charge 130 having
at least 2 lbs. of the C4 explosive is located within the
15 300-foot diameter 125 of a second charge 120. Thus, upon
the detonation of primary charge 130, all of the
explosives on the bridge will be detonated either by the
devices 120 sensing the initial primary explosion, or by
sensing a secondary explosion within its 300-foot diameter
20 or 150-foot range 125.
Embodiment 120 of the present invention was
specifically designed to work with the explosive C4 as it
is a standard explosive used by military demolition units.
Particularly, it was designed to detonate upon sensing a
minimum of 2 lbs. of C4 explosive being detonated within
a 150 foot radius; however, device 120 may be used with
other powerful explosives. It was found that powerful
explosives upon detonation, have a specific acoustic
freguency which can be detected. For C~ that frequency
range is between .2 hertz and 500 hertz having a specific
acoustic threshold level which can be calculated from
acoustic measurements of the C4 explosive when detonated.
Embodiment 120 was tested to ensure that it would
properly discriminate between the C4 explosive and small
arms fire, such as a 30-06 rifle or a 12-gauge shotgun at
30 and 100 feet respectively. Secondly, the invention was
tested to insure that a medium caliber weapon such as 25mm
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and 30mm automatic cannons fired at 30 and 100 feet,
respectively, and a large gun, (e.g., a 155mm Howitzer),
Pired at a 130 feet would not induce a false detonation.
Due to the different acoustic frequencies and the
threshold levels, this invention is able to distinguish
each of these noise signals. Because th~ C4 explosive has
a low frequency acoustic signal upon detonation, line of
sight location for device 120 detonation is not required.
This is due to low frequency signals being able to
traverse obstacles more efPectively than high frequencies.
Figure 2 is a drawing o~ embodiment 120 the
present invention as a finished product. The basic device
i6 encased in an acoustically sealed box 200 with a
microphone (not shown) located directly behind a sintered
porous metal filter 205. Porous metal filter 205
functions as a barrier to the environment, for example,
rain, dust, sand, insects and items that could damage the
electronics. Further, metal filter 205 is an acoustic
attenuator, attenuating the acoustic pressure wave created
by the explosion of the primary charge. A Pacific Metals
(located in hos Angeles, California) FCR-25 porous metal
filter is used in this embodiment. The openings in the
metal filter vary from .0005 to .001 inch.
By incorporating acoustiGally sealed box 200 and
porous metal filter ~05 (e.g., having the form of a metal
diaphragm), seismic pressure waves are attenuated at a 10
to 1 level. Seismic pressure waves are signals that are
passed through solid materials (e.g., the ground) and,
unless attenuated, they may cause false detonation.
Porous metal filter 205 diminishes the possibility of
false detonation.
Acoustically sealed box 200 has been demonstrated
to protect device 120 Prom damage due to a blast of as
much as 10 lbs. of C4 within 20 ~eet. Thus, the sensor
has the capability to survive and perform its primary
function of detection, and has the feasibility of a
reusable device for training purposes provided that the
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training unit is designed to utilize replaceable
batteries.
Figure 3 is a schematic of the electrical
aomponents of the present invention. ~his schematic i6
divided into three major part--a sensor means 310, a logic
means 340 and an output circuit 370. Additionally, there
is a blasting cap 395, two crystal oscillators 343 and
345, an energy supply 305, being two AA size batt2ries,
and an initializing switch 306. The two A~ size batteries
305 supply energy for the entire circuit used to detonate
blasting cap 395.
The sensor circuit comprises a microphone 320, a
bia~ circuit 325, a gain means 323, a ~ilter 327, and a
detection circuit 335. Microphone 320 is placed directly
behind porous metal filter 205 of ~igure 2. Microphone
320 senses the initial explosion of the primary charge or
a secondary charge. Upon sensing the detonation of the
primary charge, microphone 320 passes a first signal to
bias circuit 325. B-las circuit 325 provides feedback to
microphone 320 in order to keep microphone 320 operating
at its optimum level. Bias circuit 325 passes the signal
from microphone 320 to gain circuit 323 and filter circuit
327. Gain circuit 323 increases the level of the signal
sensed by microphone 320 to an adequate level which is
usable by the remainder of the circuit. Filter 327 is a
bandpass filter 327 which permits sound having a frequency
from 0.2 hertz to 500 hertz to pass to detector 335.
Detector 335, upon sensing tha signal from filter 327,
determines whether the signal is above a set threshold
level. If the signal is above the set threshold, detector
335 continues to process the signal to output control 355
of logic means 340. Sensor circuit 310 is described in
greater detail below in conjunction with Figure 4.
Logic means 340 comprises an output control 355,
two counters 350 and 352, two low power oscillators 342
and 344, a self-check 365, a slow-check 362 and a fast-
check 360. Logic means 3~0 has two primary functions.
First, logic means 340 passes the fire signal from sensor
means 310 to output circuit 370. Second, logic means
functions as a safety feature to prevent premature ~iring
of blasting cap 395.
Logic means 340 is incorporated into a LSIC
tlarge scale integrated circuit) in order to decrease the
overall size and weight of the unit. In connection with
the large scale integrated circuit, two crystal
oscillators 343 and 345 have been provided. Upon
initiation by initiating switch 306, crystal oscillators
343 and 345 oscillate and pass their signals to low power
oscillators 342 and 344. ~irst and second low power
oscillators 3~2 and 344 are utilized to ensure that proper
timing functions exist. First low power oscillator 344 is
a primary time base. The output of primary time base 344
is provided to a first counter 352, slow-check means 362
and fast-check means 360. Second low power oscillator 342
is a test time base. The output of second low power
oscillator 342 is provided to a second counter 350, slow-
check 362 and fast-check means 360. First and second
counters 350 and 352 are utilized to count out a first
event time and a second event time. The first event time
occurs approximately ten minutes after the initializa~ion
by switch 306. The first event time trigger prevents
output control 355 from passing a fire signal from sensor
means 310 to output circuit 370 until the 10 minute tims
period has elapsed. This first event time trigger is
incorporated for the purposes of safety for the operator.
Thus, by preventing the device from firing within the
first ten minutes a~ter initialization, the operator is
able to place the entire system on the object to be
destroyed and still have an adequate time to leave the
area before the device is capable of detonating.
Counters 350 and 352 further count out a second
event time. The second event time is several hours and
upon the elapse of the second event time, output control
355 sends a fire signal to output circuit 370. The
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purpose of the second event time is to ensure that the
device activates after a predetermined period of time in
order to remove any explosives which may be harmful to
friendly forces.
Further, logic means 340 incorporates a self-
check means. The self-check means has a fast-check means
360, a slow-check means 362 and an overall sel~-check 365.
Fast-check means 360 detects the output from both primary
time base 34~ and test time baæe 342. Fast-check means
360 compares both signal~ and determines whether either
signal is oscillating at an unacceptably high level.
Slow-check means 362 detects the signal from both primary
time base 344 and test time base 342 and ensures that both
signals are 06cillating at an appropriate level. Outputs
from both slow-check means 362 and fast-check means 360
are input into self-check 365. Self-check 365 receives
signals from slow-check means 362, fast-check means 360,
a battery check 307 and a capacitor sense 308. Battery
check 307 ensures that the batteries 305 have a sufficient
energy level. Capacitor sense 208 ensures that output
circuit 370 is not energized prematurely. Upon receiving
an adequate signal from battery check 307, capacitor sense
308, slow check means 362 and fast-check means 360, self-
check 365 passes a signal to output control 355 and thus
allows output control 355 to pass the fir~ signal.
Without the presence of a positive signal from self-check
365, output control 355 can not pass the fire signal.
Further, upon receiving the signals ~rom cap sense 308,
battery check 307, slow-check means 362 and fast-check
30 means 360, self-check 365 provides a signal to a light
emitting diode 368 which informs the operator that the
device passed the self-check. This occurs within the
first ~ew minutes after initiation by initiation switch
306.
As explained above, output control 355 provides
the fire signal to output circuit 370. Further, output
control 355 provides the supply voltage for output circuit
370 from battery 305. Output control 355 will provide a
fire signal to output circuit 370 if one of two following
conditions is met. The first condition is that a first
event trigger has been received from both first and second
counters 350 and 352, a positive sel~-check has been
received ~rom self-check 365 and a fire signal has been
received from sensor means 310. The second condition is
that a positive self-check has been received from self-
check 365 and the second event trigger has been received
from fir6t and second counters 350 and 352.
Output circuit 370 of this device is common in
the art. The output circuit comprises a transistor power
switch 380 and an RC charging and eneryy storage circuit
376. Output control 355 provide power to a capacitor in
filter 376 after the 10 minute ~irst event time. Then
output control 355 provides a fire signal to txansistor
switch 380. ~nergy from the capacitor in filter 376 is
then passed through circuit 380 into blasting cap element
395 which detonates. Detonation of the blasting cap 395
causes the detonation of an explosive means, not shown in
Figure 3.
Another safety feature is imposed with FETS 385
and 390. A release signal from first counter 352 to first
FET 385 (approximately 10 minutes after initialization of
the device) must be received and a release signal from
second counter 350 to second FET 390 must also be
received. If these signals are not present, the system
will not fire. This further protects the operator from an
accidental firing.
Figure 4 is a more detailed schematic of the
sensor means 310 shown in Figure 3. Sensor means 310
comprises a microphone 420, a bias circuit 430, a filter
427, gain circuit 450, integrating circuit 460, and a
detector means 435. Microphone 420 is a BL1785 microphone
manufactured by Knowles Microphone Company (located in
Franklin ParX, IL). Microphone 420 receives a positive
supply voltage from battery 405 and has both an input 421
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and an output 422. Output 422 of microphone 420 iz
provided to gain and bias circuit 430.
Bias circuit 430 incorporates a voltage limiting
circuit. ~he voltage limiting circuit is comprised o~ t~Jo
pairs of lN4148 diodes 431, 432, 433 and 434,
respectively. The first pair, 431 and 432, are
electrically connected cathode-to anode with the anode of
fir3t diode 431 connected to output 422 of microphone 420,
the cathode of first diode 431 connected to the anode of
second diode 432 and the cathode of second diode 432
connected to the case ground 49g. A~ to the second diode
pair, the cathode of first diode 433 is connected to
output 422 of microphone 420, the anode of first diode 433
is connected to the cathode of second diode 434 and the
anode of second diode 434 is connected to case ground 499.
Gain circuit 450 for sensor means 310 comprises
a non~inverting amplifier 452 with the positive input of
operational amplifier 452 receivi~g a signal directly from
the output of microphone 420. The negative intput of
operational amplifier 452 is electrically connected to a
voltage divider. Resistors 455 and 456 are connected in
series from the positive supply voltage to the negative
supply voltage. The junction of resistors 455 and 456 is
connected to the negative input of operational amplifier
452. Operational amplifier 452 further has a negative
feedback resistor 457~ The output of operational
amplifier 452 is electrically provided to integrating
amplifier 460 and passive bandpass filter 427.
Integrating amplifier 460 is used as a feedback network to
3U microphone 420. The output of integrating amplifier 460
is feed through resistor 462 back to microphone 420. This
feedback provides the biasing noted above. Further, the
output of integrating ampli~ier 460 is fed back to the
positive input of non-inverting amplifier 452, thereby
reducing the DC offset and centering the output of non-
inverting amplifier 452.
Passive bandpass filter 427 comprise~ a network
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with terminals A, B and C and the circuit is made up o~ a
pair of resistors 470 and 471 and a pair of capacitors 473
and 474. Resistor 470 is electrically connected between
terminals A and B and second resistor 471 is electrically
5 connected between terminals B and C. Capacitsr 473 is
electrically connected between terminals B and ground and
second capacitor 474 is electrically connected between
terminals C and ground. The input terminal for passive
filter 427 is terminal A, which is connected to the output
10 of non-inverting amplifier 452. Terminal C, being the
output of the passive filter 427, is input into detection
means 435. Detection means 435 comprises a comparator
amplifier 480 and resistors 481, 482 and 483. Resistor
483 is a hysteresis resistor, which is electrically
15 connected between the positive input of comparator
amplifier 480 and the output of comparator amplifier 480.
The threshold level is set by connecting resistors 481 and
482 in series ~rom case ground 499 to system ground 498.
The junction of resistors 481 and 482 is conncted to the
20 negative input of comparator amplifier 480. In this
manner, if the output of passive filter 427 is of
sufficient strength, it will trigger comparator amplifier
480 to output a fire signal to logic means 340 of Figure
3.
As has been shown, the present invention
overcomes the limitations of the prior art. By
incorporating the acoustic sensor, this device no longer
requires the physical connections, such as detonation
cord, and further is not susceptible to electromagnetic
interference which affected prior art devices. Further,
due to the specific characteristics of the acoustic
signals of an explosive, the present invention is capable
of discriminating normal background noises from the
specific signal of the primary explosive. This enables
the operator to quickly place the system on the object to
be destroyed with a reduced chance of detection, thereby
eliminating the dangers of prior art devices.
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